Provide a module:compositionComplete event and...

use it instead of misc other hooks.

- Extracted Keyboard-related stuff into keyboardHandler.js,
Scrollbar-related stuff into scrollState.js and code related to stock
templates into stockTemplate.js.
- Show Preview in ContentPart Editor.
- Fixed NullReference-Bug in DbFileUploadController.
- Reload files in draft editor after they got replaced.
- Misc visual fixes.
Improved handling of dirty-state and validation...

... errors in draft editor.
Added Preview for drafts and draft content parts.

Show Tooltips in Markdown editor. Fixed misc visual bugs.